1. Field of the Invention
This invention relates to improvements in a plasma etcher which utilizes a glow discharge plasma.
2. Brief Description of the Prior Art
In recent years, in order to cope with high densities of packaging of semiconductor integrated circuits, the development of the fine pattern delineation technology exploiting a radio frequency glow discharge has been vigorously promoted. This method is such that a low pressure gas containing a hologen is introduced into a vacuum chamber, an r.f. field is applied to convert the low pressure gas into a plasma, and the surface of a sample is etched and worked by active ions or radicals in the generated plasma. This method is generally referred to as a "dry etching process."
As compared with the conventional wet etching process employing a liquid, this method has the advantage that a fine pattern can be delineated with high precision; whereas, it has the disadvantage that the uniformity of etching is often insufficient. The causes for the non-uniform etching relate to various factors, such as non-uniformity in the r.f. field, non-uniformity in the stream of gas and non-uniformity in the concentrations of etching reaction products.
The inventors have found out that, in the case where an outlet for the gas is connected directly with the etching chamber, as in the prior art plasma etcher, the stream of gas towards the outlet becomes non-uniform, so the distribution of etching rates becomes particularly non-uniform.
A schematic view for explaining an example of the prior art apparatus in which the outlet is connected directly with the etching chamber in this manner is shown in FIG. 1. The apparatus illustrated in FIG. 1 is the so-called parallel plate diode type plasma etcher which includes two plate electrodes 1 and 2 within an etching chamber 6. The electrode 2, for example, is supplied with r.f. power from an r.f. power source 5, to generate a plasma within the etching chamber 6. A gas to be turned into the plasma is introduced through a gas inlet 3 provided in one of the sidewalls of the etching chamber, and it is discharged through a gas outlet 4 provided in the other sidewall.
Using the prior art apparatus, the inventors investigated the distribution of etching rates on the electrode 2 in the case where an Al specimen arranged on the electrode 2 and having a diameter of 35 cm was etched by introducing BCl.sub.3 gas into the etching chamber 6 at a flow rate of 50 ml/min. to set the pressure within the etching chamber 6 at 0.15 Torr and then applying r.f. power to generate a plasma. As a result, it has been revealed that the etching rates of Al are non-uniform on the electrode and that they are conspicuously non-uniform especially in the vicinity of the gas outlet. The non-uniformity amounted to .+-.10% or so. It is added that this finding has not been published yet.
The following references are cited to show the state of the art:
(i) Japanese Published Unexamined Patent Application No. 52-91745, PA1 (ii) Japanese Published Unexamined Patent Application No. 52-132677, and PA1 (iii) Japanese Published Unexamined Patent Application No. 54-11676.